read well, naruto was unconscious not dead. first off remember that naruto is essentially ashura, therefore he has ashura's massive amounts of chakra and vitality and what not. you also have to remember that kushina was considered special, even for an uzumaki and was recruited specifically to become the jin of the kyuubi. also remember, naruto had been fighting non stop ever since he left the island, not to mention he was training before that. kushina on the other hand gave birth and thats it, but she still looked like death. do you also realize that his mother is uzumaki? thus him having uzumaki blood. karin gets shitted on.